streamrip-go/internal/audio/convert/convert.go

package convert

import (
	"fmt"
	"os"
	"os/exec"
	"path/filepath"
	"sort"
	"strconv"
	"strings"

	"streamrip-go/internal/config"
)

type profile struct {
	codecLib string
	ext      string
	lossless bool
}

var profiles = map[string]profile{
	"FLAC":   {codecLib: "flac", ext: "flac", lossless: true},
	"ALAC":   {codecLib: "alac", ext: "m4a", lossless: true},
	"OPUS":   {codecLib: "libopus", ext: "opus", lossless: false},
	"MP3":    {codecLib: "libmp3lame", ext: "mp3", lossless: false},
	"VORBIS": {codecLib: "libvorbis", ext: "ogg", lossless: false},
	"AAC":    {codecLib: "aac", ext: "m4a", lossless: false},
}

func Convert(path string, cfg config.ConversionConfig) (string, error) {
	if !cfg.Enabled {
		return path, nil
	}
	if _, err := exec.LookPath("ffmpeg"); err != nil {
		return path, fmt.Errorf("ffmpeg not found: %w", err)
	}

	p, ok := profiles[strings.ToUpper(strings.TrimSpace(cfg.Codec))]
	if !ok {
		return path, fmt.Errorf("unsupported conversion codec: %s", cfg.Codec)
	}

	base := strings.TrimSuffix(path, filepath.Ext(path))
	finalPath := base + "." + p.ext
	tmpPath := finalPath + ".tmp." + p.ext

	args := buildFFmpegArgs(path, tmpPath, p, cfg)
	cmd := exec.Command("ffmpeg", args...)
	output, err := cmd.CombinedOutput()
	if err != nil {
		_ = os.Remove(tmpPath)
		return path, fmt.Errorf("conversion failed: %w: %s", err, string(output))
	}

	if path != finalPath {
		_ = os.Remove(path)
	}
	if err = os.Rename(tmpPath, finalPath); err != nil {
		_ = os.Remove(tmpPath)
		return path, err
	}

	return finalPath, nil
}

func buildFFmpegArgs(inputPath, outputPath string, p profile, cfg config.ConversionConfig) []string {
	args := []string{
		"-y",
		"-i", inputPath,
		"-map", "0:a:0",
		"-map_metadata", "0",
		"-c:a", p.codecLib,
	}

	if p.lossless {
		filter := buildLosslessFilter(cfg)
		if filter != "" {
			args = append(args, "-af", filter)
		}
	} else {
		if cfg.LossyBitrate > 0 {
			args = append(args, "-b:a", strconv.Itoa(cfg.LossyBitrate)+"k")
		}
	}

	args = append(args, outputPath)
	return args
}

func buildLosslessFilter(cfg config.ConversionConfig) string {
	parts := make([]string, 0, 2)
	if cfg.SamplingRate > 0 {
		rates := allowedSampleRates(cfg.SamplingRate)
		if len(rates) > 0 {
			parts = append(parts, "sample_rates="+strings.Join(rates, "|"))
		}
	}
	if cfg.BitDepth == 16 {
		parts = append(parts, "sample_fmts=s16p|s16")
	} else if cfg.BitDepth == 24 || cfg.BitDepth == 32 {
		parts = append(parts, "sample_fmts=s16p|s16|s32p|s32")
	}
	if len(parts) == 0 {
		return ""
	}
	return "aformat=" + strings.Join(parts, ":")
}

func allowedSampleRates(max int) []string {
	all := []int{44100, 48000, 88200, 96000, 176400, 192000}
	out := make([]int, 0, len(all))
	for _, r := range all {
		if r <= max {
			out = append(out, r)
		}
	}
	sort.Ints(out)
	str := make([]string, 0, len(out))
	for _, r := range out {
		str = append(str, strconv.Itoa(r))
	}
	return str
}